Electrical switch

ABSTRACT

An electrical switch for electrical tools having an electric motor operated by a DC voltage. The switch comprises a contact system including a stationary contact and a switching contact, an operating element which acts on the switching contact to initiate a process for switching the contact system between an on-position and an off-position and a shield that quenches an arc that occurs between the stationary contact and the switching contact during the switching process. A movable slide is operatively connected to the operating element and has the switching contact arranged thereon. During the process of switching the switching contact from the on-position to the off-position, the shield is moved to an area located between the stationary contact and the switching contact. During the process of switching the switching contact from the off-position to the on-position, the shield is moved from the area located between the stationary contact and the switching contact. The shield is joined at one end to the slide, and the other end of the shield operates as a shielding element for the switching contact. The shield moves positively with the slide into and out of the area between the switching contact and the stationary contact.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrical switch for electric toolshaving an electric motor operated by a DC voltage.

2. Description of Prior Art

Electrical switches such as these are used in particular as mainsswitches for electrical handheld tools. Particularly in the case ofelectric motors which are operated by means of a DC voltage, for example125 volts, heavy currents can flow, for example a direct current of 130Amperes or more, so that an arc occurs between the contacts on switchingoff. The occurrence of arcs can lead to the switch being destroyed, andthis must be prevented, for safety reasons, in electrical tools.

DE 197 26 402 A1 discloses an electrical switch for heavy currents,which is provided with means for quenching an arc. This switch has acontact system which comprises a stationary contact and a switchingcontact. An operating element acts on the switching contact in order toinitiate a process for switching the contact system between anoff-position and an on-position. The means, which is associated with thecontact system and is in the form of a shield, for quenching any arcwhich occurs between the stationary contact and a switching contactduring the switching process is movably coupled to the switchingcontact. In consequence, the shield is moved into the area locatedbetween the stationary contact and the switching contact during theprocess of switching the switching contact from the on-position to theoff-position, and is moved out of the area located between thestationary contact and the switching contact during the process ofswitching the contact from the off-position to the on-position.

When switching the contact system on, the shield is moved downward, sothat the shield is located underneath the stationary contact when in theon-position. A certain amount of space is therefore required there inthe housing of the switch, for which purpose the housing has a bulge inthis area. In some applications, particularly when there is a shortageof space available in the handle of the electrical appliance, thisbulging in the switch housing may cause interference. Furthermore, thecoupling between the switching content and the shield involves a complexdesign, resulting in the shield moving in a complicated way whenswitching between the off-position and the on-position. Thisnecessitates high precision for production of the parts for the shieldand, in the end, this increases the production costs for the switch.

SUMMARY OF THE INVENTION

The invention is based on the object of developing the shield further insuch a manner that the switch housing can be further reduced in size.

For a switch of this generic type, this object is achieved by anelectrical switch for electrical tools having an electric motor operatedby a DC voltage, comprising: a contact system including a stationarycontact and a switching contact; an operating element which acts on theswitching contact to initiate a process for switching the contact systembetween an on-position and an off-position; a shield that quenches anarc that occurs between the stationary contact and the switching contactduring the switching process; a movable slide being operativelyconnected to the operating element and having the switching contactarranged thereon; wherein, during the process of switching the switchingcontact from the on-position to the off-position, the shield is moved toan area located between the stationary contact and the switching contactand, during the process of switching the switching contact from theoff-position to the on-position, the shield is moved from the arealocated between the stationary contact and the switching contact; andwherein one end of the shield is moveably associated to the slide andthe other end of the shield operates as a shielding element for theswitching contact, when the shield is moved to the area between thestationary contact and the switching contact.

In one preferred development, the shield is in the form of a two-armedlever element. The first lever arm of the lever element is articulatedon the slide, and the second lever arm is associated with the switchingcontact, as the actual shielding element. The two-armed lever elementmay be approximately C-shaped or sickle-shaped. The switch housing maycomprise a housing lower part for holding the slide, the contact systemand the like, and the housing upper part in the nature of a cover. Inthis case, the rotation part of the two-armed lever, may be mounted inthe interior of the housing, in particular on the housing lower part.

In order to articulate the shield on the slide, a guide link is locatedin the slide and/or in an attachment arranged on the slide. A bolt whichis fitted to the first lever on the shield engages in the guide link insuch a manner that the shield can be moved positively with the slide.The guide link may comprise a first guide surface, facing the switchingcontact, and a second guide surface, which is adjacent to it and facesaway from the switching contact. The first guide surface is in the formof an inclined plane, which runs obliquely with respect to the movementdirection of the slide, while the second guide surface runsapproximately in the direction of movement of the slide. Overall, theguide link is approximately boomerang-shaped. This type of articulationensures precise positive guidance between the slide and the shield.

The housing lower part has a recess for holding at least one part of thesecond lever arm of the shield when the contact system is in theon-position. Furthermore, the recess is also used for holding part ofthe first lever arm of the shield when the contact system is in theoff-position. At least one side surface can be arranged on the secondlever arm, which acts as the shielding element, in such a manner thatthe shielding element forms a type of cap. The cap then largely coversthat surface of the switching contact which faces the stationary contactin the off-position. This refinement reliably prevents the arc fromescaping sideways.

In one preferred refinement, the switch according to the invention has acontact system with two stationary contacts and one switching contactwhich is in the form of a bridging contact and is provided with twocontact surfaces. The shield comprises two lever elements which arearranged alongside one another and are associated with the respectivecontact surface. The two lever arms of the lever element of the shieldcan be connected to one another at their rotation point via a commonshaft. The shaft expediently has ends which project at the rotationpoint of the lever element, with the two ends of the shaft each beingmounted in a holder in the housing lower part such that they can rotate.Furthermore, two mutually opposite attachments can be arranged on theslide, each having a guide link, in such a manner that the bolt on thefirst lever arm of each lever element engages in the guide link.

The advantages achieved by the invention are, in particular, that theswitch is reliably protected against its contact system being destroyedby the influence of arcs. Any arc which may occur is quenched within ashort time, thus effectively preventing erosion of the contacts in thecontact system. The life of the switch is thus considerably increased.

The electrical switch is particularly suitable for heavy currents andcan thus be used in high-powered electrical tools. In particular, theswitch can be used for electric motors which are operated with DCvoltage, where, in contrast to the situation at the zero crossing of anAC voltage, the arc is not automatically quenched. The switch can alsobe used as a brake switch for electrical tools that use short-circuitbreaking, where particularly large direct currents occur on switchingoff, due to the electric motor being short-circuited and acting as agenerator.

BRIEF DESCRIPTION OF THE DRAWINGS

Nevertheless, the switch is compact and physically small overall, and itis thus particularly suitable for narrow, ergonomic handles on electrictools. In addition, the shield has a simple design so that no particularprecision is required for producing the parts for the shield.Furthermore, only a small number of additional parts are required forthe switch, while its functionality is improved. In consequence, onlyminor additional production costs are incurred for the switch, despiteits performance being improved.

An exemplary embodiment of the invention, together with developments,will be described in more detail in the following text and isillustrated in the drawings, in which:

FIG. 1 shows a longitudinal section through an electrical switch, withthe contact system being in the off-position,

FIG. 2 shows an enlarged detail of the contact system corresponding tothe region II shown in FIG. 1,

FIG. 3 shows a longitudinal section through the electrical switch, withthe contact system being in the on-position,

FIG. 4 shows an enlarged detail of the contact system as in FIG. 2, withthe contact system being in the on-position, corresponding to the regionIV in FIG. 3, and

FIG. 5 shows the slide with the shield as an individual part, as aperspective view seen from underneath.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an electrical switch 1 which can be used as a mains switchin an electrical handheld tool, such as an angle grinder, a drill, acircular saw or the like. The electrical handheld tool contains anelectric motor which is operated, for example, by means of directcurrent.

The switch 1 has a housing 2 which comprises a housing lower part 14 inthe nature of a base, and a housing upper part 15 in the nature of acover. At least one contact system 3 is arranged in the interior of thehousing 2. This switch 1 contains two contact systems 3, 3 a, forswitching two current paths. The contact system 3, 3 a comprises astationary contact 4, which is fitted to an electrical connection 29that is used for connection to electrical supply lines in the electricaltool, and a switching contact 5. In particular, in a switch 1 such asthis, the contact system 3, 3 a may in each case have two fixed contacts4, 4′ and a switching contact 5 which is in the form of a bridgingcontact and is provided with two contact surfaces 24, 24′, as can beseen in FIG. 5.

An operating element 6, arranged on the housing 6, acts on the switchingcontact 5 in order to initiate the process of switching the contactsystem 3, 3 a from an off-position to an on-position. For this purpose,the operating element 6 is operatively connected to a slide 8 which islocated in the housing 2 and can be moved essentially linearly, in thata plunger 30, which projects out of the housing 2, of the slide 8 isarticulated on the operating element 6. The slide 8, the contact system3, 3 a and, possibly further parts of the switch 1 are held in thehousing lower part 14. The slide 8 and the plunger 30 contain springs31, 32 and another pressure-point spring, which is not shown, so thatthe slide 8 switches in the form of a snap-action movement between thetwo positions of the contact system 3, 3 a. For its part, the switchingcontact 5 is arranged with an elastic element 11 on the lower face ofthe slide 8, as can be seen in FIG. 1 or 3. The configuration of theoperative connection between the slide 8 and the operating element 6 isdescribed in more detail in DE 199 30 558 A1 from the same applicant,which was not published prior to this and is itself based on thepriority of German Patent Application DE 198 33 296.3, so that anyfurther description is superfluous at this point.

The following text will consider only the contact system 3 in moredetail, with respect to the invention. The contact system 3 can be seenin the off-position in FIGS. 1 and 2, in which the switching contact 5is at a distance from the stationary contact 4. FIG. 3 and FIG. 4 showthe contact system 3 in the on-position, in which the switching contact5 and the stationary contact 4 are in contact. As can be seen inparticular from FIG. 4, the elastic element 11 then exerts a forcepressing the switching contact 5 against the stationary contact 4.

When operating high-power electric motors, correspondingly heavycurrents flow via the contact system 3 of the switch 1 when it is in theon-position. For example, a direct current of up to approximately 120Amperes can flow in angle grinders whose power is 2.3 kilowatts. Whenthe electric motor is switched off, that is to say when the contactsystem 3 is switched to the off-position, an arc is then struck betweenthe switching contact 5 and the stationary contact 4, and this can leadto contact erosion. In order to avoid destruction of the contact system3, the contact system 3 has associated means, which are in the form of ashield 7, for quenching any arc which occurs between the stationarycontact 4 and the switching contact 5 during the switching process.

The shield 7 is coupled to the switching contact 5 such that it canmove. As can be seen in FIG. 2 or 4, one end 9 of the shield 7 isarticulated on the slide 8 for coupling, and the other end 10 isassociated with the switching contact 5, as the shielding element. Thiscoupling results in the shield 7 moving into the area located betweenthe stationary contact 4 and the switching contact 5 during the processof the switching contact 5 from the on-position shown in FIG. 4 to theoff-position shown in FIG. 2, so that the arc is displaced orinterrupted, and is finally quenched. During the opposite process whenthe switching contact 5 is switched from the off-position shown in FIG.2 to the on-position corresponding to FIG. 4, the shield 7 is moved outof the area located between the stationary contact 4 and the switchingcontact 5. Since the shield 7 is then located outside this area betweenthe switching contact 5 and the stationary contact 4, the switchingcontact 5 can make contact with the stationary contact 4 without anyimpediment in the on-position.

More details of the configuration of the shield 7 can be seen in FIG. 2or 4. The shield 7 is in the form of a two-armed lever element 28. Thetwo-armed lever element and the shield 7 is preferably approximatelyC-shaped or sickle-shaped like a toggle lever. The one, first lever arm12 is articulated on the slide 8, while the other, second lever arm 13is associated with the switching contact 5, as the actual shieldingelement. At least one side surface 23 can be arranged on the secondlever arm 13, which acts as the shielding element, and this can be seenparticularly clearly in FIG. 4, so that the shielding element then formsa type of cap. This cap largely covers that contact surface 24 of theswitching contact 5 which faces the stationary contact 4 in theoff-position, corresponding to FIG. 2, whilst preventing the arc fromescaping sideways. The rotation point 16 of the two-armed lever element28 of the shield 7 is mounted in a holder 27, such that it can rotate,in the interior of the housing 2, to be precise on the housing lowerpart 14.

The configuration of the articulation of the shield 7 on the slide 8 canlikewise be seen in more detail in FIG. 2 or 4. For this purpose, theslide 8 has a guide link 17, which may be located in an attachment 18,which is arranged on the slide 8 and can be seen in FIG. 5. The guidelink may also be located directly in the slide 8, of course, but this isnot shown in any more detail. A bolt 19 which is fitted on the firstlever arm 12 of the shield 7 engages in the guide link 17 in such amanner that the shield 7 can be moved positively with the slide 8. Theguide link 17 itself comprises a first guide surface 20, which faces theswitching contact 5 and is in the form of an inclined plane, and asecond guide surface 21, which is adjacent to it and faces away from theswitching contact 5. The first guide surface 20 runs essentiallyobliquely with respect to the movement direction of the slide 8, whilethe second guide surface 21 runs approximately in the direction ofmovement of the slide 8. The guide link 17 is thus approximatelyboomerang-shaped.

The housing lower part 14 has a recess 22, which can be seen in FIGS. 1to 4. The recess 22 is used to hold at least one part of the secondlever arm 13, which is in the form of a shielding element of the shield7 when the contact system 3 is in the on-position, as can be seen inFIG. 4. Furthermore, as can be seen in FIG. 2, the recess 22 is alsoused to hold a part of the first lever arm 12 of the shield 7 when thecontact system 3 is in the off-position.

If the switching contact 5 is provided with two contact surfaces 24, 24′as the bridging contact, then it is possible for the shield 7 to becomposed of two lever elements 28, 28′, which are arranged alongside oneanother and are associated with the respective contact surface 24, 24′.Such a configuration is shown in more detail in FIG. 5, as an explodedillustration of the slide 8 and the shield 7. The two lever elements 28,28′ are connected to one another at their rotation point 16 via a commonshaft 25. The shaft 25 furthermore has ends 26 which project at therotation point 16 of the lever elements 28, 28′, with the two ends 26 ofthe shaft 25 each being mounted such that they can rotate in a holder27, which is indicated in FIG. 2 or 4, in the housing lower part 14. Twomutually opposite attachments 18, 18′ are arranged on the slide 8 andeach have a guide link 17, in such a manner that the bolt 19 on thefirst lever arm 12 of each lever element 28, 28′ engages in the guidelink 17. The two lever elements 28, 28′ are thus positively guided atthe same time during movement of the slide 8, and their second leverarms 13 act in the manner described above as shielding elements for thetwo contact surfaces 24, 24′ of the switching contact 5, in order tointerrupt the arc.

The invention is not restricted to the exemplary embodiment which hasbeen described and illustrated. In fact, it also covers all specialistdevelopments within the scope of the idea of the invention. Theinvention can thus be used not only, for switches for electrical toolsbut also for switches for controllers, for example in the field of motorvehicles or the like.

What is claimed is:
 1. An electrical switch for electrical tools havingan electric motor operated by a DC voltage, comprising: a contact systemincluding a stationary contact and a switching contact; an operatingelement which acts on the switching contact to initiate a process forswitching the contact system between an on-position and an off-position;a shield that quenches an arc that occurs between the stationary contactand the switching contact during the switching process; a movable slidebeing operatively connected to the operating element and having theswitching contact arranged thereon; wherein, during the process ofswitching the switching contact from the on-position to theoff-position, the shield is moved to an area located between thestationary contact and the switching contact and, during the process ofswitching the switching contact from the off-position to theon-position, the shield is moved from the area located between thestationary contact and the switching contact; and wherein one end of theshield is moveably associated to the slide, and the other end of theshield operates as a shielding element for the switching contact, whenthe shield is moved to the area between the stationary contact and theswitching contact.
 2. An electrical switch according to claim 1, whereinthe slide is located in a housing of the switch and moves substantiallylinearly, and when the contact system is in the on-position, an elasticelement arranged in the slide exerts a force pressing the switchingcontact against the stationary contact.
 3. An electrical switchaccording to claim 1, wherein the shield is in the form of a two-armedlever element, with the first lever arm being joined to the slide, andthe second lever arm being associated with the switching contact as theactual shielding element.
 4. An electrical switch according to claim 3,wherein the two-armed lever element is substantially C-shaped orsickle-shaped.
 5. An electrical switch according to claim 3, wherein thehousing of the switch comprises a housing lower part in the form of abase for holding at least the slide and the contact system and a housingupper part in the form of a cover, so that a rotation point of thetwo-armed lever element is mounted on the housing lower part in theinterior of the housing.
 6. An electrical switch according to claim 5,wherein the housing lower part has a recess for holding at least onepart of the second lever arm when the contact system is in theon-position and for holding a part of the first lever arm when thecontact system is in the off-position.
 7. An electrical switch accordingto claim 3, wherein a guide link is located in at least one of the slideand an attachment arranged on the slide, and a bolt is fitted to thefirst lever arm of the shield for engaging in the guide link and joiningthe shield to the slide, so that the shield moves positively with theslide.
 8. An electrical switch according to claim 7, wherein the guidelink comprises a first guide surface, which faces the switching contact,is in the form of an inclined plane and runs substantially obliquelywith respect to a direction of a movement of the slide, and a secondguide surface, which is adjacent to the first guide surface, faces awayfrom the switching contact and runs substantially in the direction ofthe movement of the slide, the guide link being substantiallyboomerang-shaped.
 9. An electrical switch according to claim 1, whereinat least one side surface is formed on the second lever arm, so that,when the contact system is in the off-position, the shielding elementforms a cap, which largely covers a contact surface of the switchingcontact that faces the stationary contact.
 10. An electrical switchaccording to claim 1, wherein the contact system comprises twostationary contacts and one switching contact, the switching contactbeing in the form of a bridging contact and being provided with twocontact surfaces, and the shield comprises two lever elements which arearranged alongside one another and are associated with a respective oneof the contact surfaces, the two lever elements being connected to oneanother at a rotation point via a common shaft, the shaft having twoends that project at the rotation point of the lever elements, each ofthe two ends of the shaft being mounted in a holder in a lower part of ahousing such that the two ends rotate, the slide having two mutuallyopposite attachments arranged thereon, each of the mutually oppositeattachments having a guide link where a bolt on a first lever arm ofeach of the two lever elements engages in the guide link.